Chemistry Reference
In-Depth Information
reduction potentials, high oxidation and thermal stability (Papaiconomou et al.
2007
,
2010
). For an IL the
reduction potential
is mostly influenced to the type of the cation:
ILs containing saturated heterocyclic cations such as pyrrolidinium (Pyr) or piperi-
dinium (Pip) are subject to reduction at much more negative potentials (
3 V versus
Ag/AgCl electrode) than ILs containing unsaturated heterocycles as imidazolium
heterocycles which are reduced below
−
−
2 V or di- or tri-substituted Py8 that are re-
ducted around
1.3 V; (Papaiconomou et al.
2010
; Appetecchi et al.
2009
;
Zhang et al.
2007
).
Oxidation potentials
is related to the electrochemical stability of
the anion, whatever the cation used. (Papaiconomou et al.
2010
; Appetecchi et al.
2009
; Ohno et al.
2005
). It was reported that presence (of more than two) methyl
groups on pyridinium cations, reduction occurs at lower potentials and increases the
oxidation potential of the IL (Papaiconomou et al.
2010
; Zhang et al.
2007
).
ILs can
solubilize
various gases (e.g. CO
2
—the most significant greenhouse gas,
which can be seen as a non-toxic C1 resources, and he have many applications
in the production of valuable products and materials) (Zhang et al.
2009
; Carrera
et al.
2010
; Deng et al.
2011
). In particular, Deng et al. (
2011
) reported that intro-
duction of oxygen functionalities or chemical modification of the alkyl side chain in
imidazolium-based ILs does not lead to significant changes of the solubility of differ-
ent families of gases, while the nitrile or vinyl groups in the cation of the IL, can lead
to ILs with interesting solvation properties (Deng et al.
2010
; Muldoon et al.
2007
;
Costa Gomes
2007
; Anthony et al.
2002
). Also they showed that the presence of the
ester and hydroxyl groups in the cation of the pyridinium- or ammonium-based ILs
not influenced the CO
2
solubility, except for the case of functionalized-pyridinium-
based ILs in which the gas is much less soluble (Deng et al.
2011
). According to
the structural features and fixation/absorption mechanisms, the ILs can be classified
into:
conventional ILs
—can absorb/fix less CO
2
because of the physical interac-
tions between CO
2
and ILs (e.g. IM14 PF
6
that can solubilize CO
2
in much higher
quantities than other gases such as CO, CH
4
,H
2
,N
2
, and ethane) and
task-specific
ILs
with alkaline groups (-NH
2
)—because of the chemical interactions or reac-
tivity between CO
2
and the alkaline groups of the ILs they can sequester larger
amounts of CO
2
than the conventional ILs (e.g. P
4444
AA). (Zhang et al.
2009
;
Carrera et al.
2010
; Anthony et al.
2002
). Poly-ILs (PILs) have good CO
2
sorption
capacities which are depending on the type of cation and anion, decreasing in the
following order: ammonium
>
pyridinium
>
phosphonium
>
imidazolium when we
discuss the cations, and [Cl]
−
>
[BF
4
]
−
>
[PF
6
]
−
>>
[NTf
2
]
=
when we discuss the
anions (Mallakpour and Rafiee
2011a
,
b
).
Due to their special properties ILs have gained attention for a wide variety of
applications such as:
solvent and catalyst
for many chemical synthesis, polymeriza-
tion reactions, nanostructures and nanomaterial technologies, enzymatic reactions
and biocatalysis;
extraction and separation
—extraction of CO
2
and metal ions (and
also media to store gases), gas or liquid chromatography and capillary electrophore-
sis;
electroanalytical applications and electrochemical devices
—lithium batteries,
fuel or solar cells, different types of (super)capacitors, electrodeposition of metals,
electropolishing of stainless steel;
sensors
—electrochemical sensors, optical sensors
and biosensors;
biopolymers
;
matrices
for matrix-assisted laser desorption/ionization
−
1.2 to
−
